The present invention relates to a new centrifugal process and device for harvesting blood platelets for transfusion. The invention provides a means for collection of platelets in a closed, sterile and disposable system and, more particularly, provides a means for procurement of a therapeutically effective dose of platelets from a single donor, as well as from multiple or random donors. This invention is an improvement of the invention, disclosed in two U.S. patents: one by Maxim D. Persidsky entitled "Process and Device for Centrifugal Separation of Platelets," U.S. Pat. No. 4,269,718, issued on May 26, 1981, and the other by Maxim D. Persidsky and Nan-Sing Ling entitled "Apparatus for Centrifugal Separation of Platelet-Rich Plasma," U.S. Pat. No. 4,268,393, issued on May 19, 1981.
Among the problems encountered in the blood component separation technology currently employed in harvesting platelets for transfusion are: low collection yield of platelets; loss of large, dense platelets (designated herein as young platelets); high contamination of collected platelets with white blood cells (WBCs); sterility problem associated with the automated plateletpheresis systems; long processing time; and high equipment and operational cost. In spite of these shortcomings, there is a growing demand for transfusion of platelets for treatment of bleeding in thrombocytopenic and thrombocytopathic patients. Transfusion of platelets is also used as replacement therapy in patients with a temporary depletion of platelets due to acute leukemia, chemotherapy, radiation therapy, and major surgical procedures. As a result, within the past decade the number of platelet units transfused annually has expanded enormously. In 1971, 413,500 platelet units were transfused in the U.S. From the survey of blood collection by AABB institutional members, more than 1,250,000 units of platelets were transfused in 1975. According to the present estimate, there will be at least 3,500,000 units of platelet concentrates transfused in the U.S. during 1980.
The process for centrifugal collection of platelets as disclosed in the two above cited U.S. patents, has the potential to resolve all the above mentioned problems. This process, representing a new type of manual plateletpheresis, was evolved from the process of centrifugal elutriation (CE). Although it bears some similarities to CE, it is different from CE in several important aspects. The separation of various size particles by CE is accomplished by the process of washing particles in the separation chamber with an exponential flare at its broad end which is oriented toward the center of rotation. Liquid medium is flowing through this chamber in the direction against the centrifugal force and forms a gradient of rapidly decreasing flow along this direction. Smaller and less dense particles are continuously washed out from the chamber while larger and denser particles are retained at various levels of their equilibria within the gradient of liquid flow. A large volume of medium is required during the separation of particles by CE.
In an experimental study using the platelet collection device in the form of either FIG. 1 or FIGS. 2 to 4 of the U.S. Pat. No. 4,269,718, platelets were harvested from whole human blood at about 90% recovery of the total blood platelets. With a chamber of 11 ml capacity of FIG. 1, the time required to separate platelet-rich plasma (PRP) from whole blood was 3 minutes while with a larger chamber of 21 ml capacity of FIGS. 2 to 4, it was 5 minutes. No WBC per 10.sup.6 cells counted was found under the microscope in PRP samples separated by either chamber. The morphology and size distribution of these platelets appeared to be similar to platelets in the control smears of whole blood. The release of adenosine triphosphate (ATP) from these platelets was on the average 33% higher than that from platelets prepared by differential centrifugation. Platelets harvested either by the differential centrifugation or by the process of the present invention were found to be similar in aggregation response induced by adenosine diphosphate (ADP) or epinephrine and similar in their serotonin secretion. In vivo study of survival of radioactive chromium-labeled autologous platelets in rabbits yielded similar results for both preparations.
Preliminary tests of the scaled-up PRP separation system of 220 ml capacity built in accordance with the design of FIG. 9 of the U.S. Pat. No. 4,268,383, yielded results similar to those obtained with the systems of smaller capacity. Platelet recovery was close to 90% of the total platelets and no WBC was detected per 10.sup.6 cells counted. The platelet morphology was found to be normal. With this system of 220 ml capacity, the time used to separate PRP took 8 to 10 minutes.
The increased release of ATP by platelets harvested with the 11-ml system can be attributed to the presence of a larger number of recovered young platelets. Young platelets are known to contain higher concentration of ATP in their granules than the old platelets. The recovery of young platelets in these preparations is further substantiated by the above morphological observations.
According to a process and device of the present invention, a conical chamber is used for the separation of PRP. The chamber is loaded with whole blood prior to centrifugation. Then it is subjected to a short period of centrifugation in order to induce the formation of a narrow zone of clear plasma at the broad end of the chamber. Thereafter, a small volume of normal saline, equivalent to that of blood plasma, is pumped gradually into the chamber at its vertex in the direction against the centrifugal force. By this action, saline filters through the loosely packed blood cells and displaces PRP while red blood cells (RBCs) and white blood cells are retained in the chamber with the aid of centrifugal force at a steady state equilibrium. Under the above conditions, blood cells form a dense cells suspension which behaves like a fluidized bed of clay particles used in industrial furnaces. This dense cell suspension acts as a depth filter which allows platelets to pass through while holding back all the other cell constituents. Thus, this process of PRP separation can be distinguished from CE in that it consists of two processes: one is the displacement process; and the other is the filtration process; whereas CE involves the process of differential washing. The PRP separation process, referred to above in the two U.S. Patents, requires only a small volume of liquid for the displacement of PRP. Therefore, it was possible to design a self-sufficient device to fit in a swinging centrifuge bucket. This device includes a collapsible container for liquid medium, a centrifugally operated pump, a separation chamber, and a collection compartment.
In addition, the present process does not involve pelleting of blood cells as it does in the case of differential centrifugation. Pelleting may release ADP from RBCs which can in turn cause platelet aggregation. Therefore, platelets harvested by the present process should be less damaged than those obtained with the differential centrifugation method.
The present system with its high collection yields of platelets and its capability to recover young platelets can potentially be of great value in transfusion service when it is fully developed. It is known that young platelets can survive longer and are expected to be more effective hemostatically than old platelets. In addition, the apparent absence of WBC in the platelets harvested by the present system would be desirable in reducing the risk of immunological complications by WBCs after repeated platelets transfusions.
All the devices illustrated in both U.S. Patents represent an open system and therefore the problems of maintaining sterility still remain.